In paper processing machines, in particular in multicolored printing presses, subassemblies are used at the end of the paper path as an extension arm that controls the depositing paper sheets on an already existing stack or which can build a new stack. To this end, there are systems, for example, that work with negative pressure and overpressure, or which operate, in a purely mechanical way, e.g., by tappets and holding down systems with rollers located above. Such mechanical systems, as describe in the publication of disclosure of patent DE 199 57 574 A1, make it possible to deposit sheets with a very high degree of precision. Fewer material-intensive members are used than with customary extension arms, whereby sufficient space is available in the area around the stack to remove the stack, to inspect it or to further process the sheets.
In the extension arm described in the patent DE 199 57 574 A1, a last pair of rollers in the paper path in particular is used as a conveyor roller pair, which is attached above a pair of tappets and a hold down device. The function of this conveyor roller pair is used in conjunction with the pair of tappets and the holding down device to deposit sheets conveyed in the area of the extension arm that fit perfectly on a paper stack or to build a new stack.
The transport roller pair can be moved by rotation and can be laterally moved in the conveying direction of the sheet. The surface of the conveyor roller has a very high friction value, while the tappets located directly below the conveyor rollers on their side facing the rollers have a very low friction value. The lateral mobility of the conveyor rollers makes it possible to correct any misalignment of a sheet, at least in its position transverse to the conveying direction. Furthermore, the lateral position of sheets on a stack can be controlled, so that, for example, offsets for differentiating between the various printing jobs within the stack can be produced.
The sheets are quickly conveyed to the stack by rotating rollers. The transfer of the rotation to the conveying rollers takes place by a drive shaft. The rollers are attached to an aluminum pipe that is connected to the drive shaft. The drive shaft can then be driven by a toothed belt.
For the lateral movement of the conveyor roller in DE 199 57 574 A1, an actuator is provided above the conveyor rollers, which drives a spindle. In order to prevent twisting, a swivel head is fastened to a spindle, which drives a rod. The rod is screwed into a non-rotating adjusting ring on the aluminum pipe of the conveyor rollers. The adjusting ring is transversely coupled to the conveyor rollers, which makes it possible to move the conveyor rollers laterally.
The rod drives the swivel head on the spindle by an opening. When a new piece of paper is to be deposited on the stack, it is necessary that the conveyor rollers be removed from the surface of the stack, for which lever arms are provided on the drive shaft.
The speed with which the conveyor rollers can be laterally moved is limited here. It can be increased, for example, via a spindle that has a larger spindle stroke. However, such an extension of the system would entail substantial cost increases.
The spindle, which effects the lateral movement of the conveyor rollers, is shown here open and unprotected. As a result, it is easily soiled, and it is also susceptible to mechanical effects. Consequently, it may be damaged or at least its function may be impaired.
The drive shaft for transferring the rotation to the conveyor rollers may be driven by means of a toothed belt. Since there may be a difference in height between the sides of the sheet stack, a tilt of the drive shaft may also be required via the conveyor rollers. This tilt may amount to 4°. Since the wheels of the tooth belt are rigidly connected with the drive shaft, this tilt is also transmitted to the flanged rim pulleys of the toothed belt wheels. As a result, the toothed belts are pushed to the edge of the flanged rim pulleys and are constantly rubbed by the tilting position. Due to the wear and tear of the toothed belt, they have to be changed often.